The development of the optic sensors is one of the fastest growing new areas in the analytical chemistry. Most of these sensors do not involve direct analyte determination, but are measuring the optical properties of a reagent attached to the fiber distal's end. This reagent is selected to possess optical properties which are changed upon interaction with the target substrate. Fiber-optics sensors which utilize immobilized reagents have been developed based on fluorescence complexation and dynamic fluorescence quenching. Both fluorescence lifetimes and excitation/emission spectra are highly affected by immobilization method and the type of a solid support attached to the reagent. Such sensor elements, mainly for determining oxygen concentrations were developed within the last few years.
A very recent U.S. Pat. No. 4,925,268 describes a sensor suitable for monitoring the concentration of oxygen or hydrogen, using an optical fiber segment having at one end a matrix comprising an indicator molecule covalently linked to a polymer. The polymer claimed is selected from the group of acrylates and methacrylates. One of the main disadvantages of these sensors is the fact that the fluorescent reagents are characterized by strong intermolecular interactions, rendering them a very poor solubility in most of the solvents and a high tendency to aggregate and crystallize with typical columnar stacking. Moreover, the molecules of the reagent tend to migrate and aggregate within the solid polymeric matrix and thus they will lose their fluorescence property.
The effect of oxygen on fluorescent material is to reduce the intensity of the emitted radiation by providing a non radiative relaxation path for excited molecules. Generally, it is relatively quite easy to prepare a solution of one of the well known polycyclic aromatic fluorescent materials, normally used for this purpose, in a solvent such as toluene and use of this solution as an indicator. Usually this solution is encapsulated in a membrane which is permeable to a gas, so that oxygen can diffuse into the solution. It is also suggested to incorporate an indicator substance into a polymer, using the same solvent. However, after the evaporation of the solvent, the indicator generally does crystallize and thus it will loose most of its oxygen sensitivity.
In order to obviate the disadvantage of decrease in the reagent's sensitivity it was suggested in the European patent No. 109,959 to use a plasticizer as a carrier material for the indicator reagent in order to remain permanently incorporated into the polymer. In addition, it is also required a solvent for the indicator.
It is an object of the present invention to provide a method for the manufacture of a sensor for the determination of dissolved oxygen. It is another object of the present invention to provide a method for the manufacture of a sensor for determination of dissolved oxygen, said sensor possessing a very high concentration of fluorescent reagent, thus increasing the sensor's life-service use.